Corrosion monitoring process and apparatus for use therein

Abstract

Corrosion of a component surface, e.g. the surface of a pipe, is monitored by monitoring the thickness, e.g. by resistance measurement, of a test element formed from the material of the component and mounted so that its exposed surface is flush with and extends over substantially all of one dimension of the component surface, e.g. substantially all round the circumference of a pipe.

We claim: 
     
       1. A method of monitoring corrosion of the surface of a component subject to a corrosive environment comprising (i) forming an elongated strip test element from the material of said component,   (ii) mounting said test element, out of contact with said component, in a surface in a housing so that one elongated surface of said test element and said surface of the housing are flush with said component surface, and are exposed to said corrosive environment, said one surface of the test element extending, in the direct of its length over substantially all of one dimension of said component surface, and   (iii) monitoring the thickness of said test element.   
     
     
       2. A method according to claim 1 in which the strip test element is machined from a sample of the component. 
     
     
       3. A method according to claim 1 in which the thickness of the test element is monitored by comparing the thickness of the test element with that of a reference element mounted adjacent to the test element but protected from exposure to the corrosive environment. 
     
     
       4. A method according to claim 1 in which the test element is formed from an electrically conductive material and the thickness of the test element is monitored by monitoring the electrical resistance of the test element. 
     
     
       5. A probe for use in monitoring corrosion of the surface of a component subject to a corrosive environment comprising (i) a housing adapted for connection in-line with said component with the surface of said housing exposed to the corrosive environment flush with said surface of the component, and (ii) an elongated strip test element, formed from the material of said component, mounted in said housing so that the test element is out of contact with the component with one elongated surface of said element flush with said surface of the housing, exposed to the corrosive environment, and extending in the direction of its length over substantially all of one dimension of said component surface. 
     
     
       6. A probe according to claim 5 wherein the test element is located in a recess in the housing and an elongated strip reference element is located in said recess between the test element and the bottom of said recess, and said reference element is protected from exposure to the corrosive environment. 
     
     
       7. A probe according to claim 6 wherein an elongated strip check element is located in the recess between the test element and the bottom of the recess. 
     
     
       8. A probe according to claim 6 wherein the elements are electrically conductive and insulant material is interposed between the elements and, where the housing is electrically conductive, between the elements and the housing. 
     
     
       9. A probe according to claim 8 wherein the test and reference elements are connected in series and leads are provided whereby an electric current may be passed through the test and reference elements in series and the potential differences across the elements may be compared, one lead being connected to the connected ends of the test and reference elements, two leads being connected to the free end of the test element, and two leads being connected to the free end of the reference element. 
     
     
       10. A probe according to claim 5 wherein the component surface is the interior surface of a pipe, the housing is annular having an internal diameter equal to that of the pipe, and the exposed surface of the test element extends substantially all round the interior circumference of the housing. 
     
     
       11. Apparatus for monitoring corrosion of the surface of a component subject to a corrosive environment comprising a probe according to claim 5 in combination with means to monitor the thickness of the test element. 
     
     
       12. Apparatus according to claim 11 in which the probe is provided with an elongated strip reference element protected from exposure to the corrosive environment, said test and reference elements being electrically conductive and insulated from one another and from the housing, where the latter is electrically conductive except possibly at one point, said test and reference elements being connected in series, and said means to monitor the thickness of the test element comprises means to pass a current through the test and reference elements and to compare the potential difference across the reference element with that across the test element.